(1) Field of the Invention
The invention relates to a parking lock control element for an automobile transmission, in particular for an automatic transmission, according to the preamble of claim 1.
Parking locks are always employed when non-mechanical components are used for transmitting drive forces in an automobile, in particular in automatic transmissions having a hydrodynamic torque converter. Automobiles with automatic transmissions are typically equipped with a parking lock to prevent the vehicle from accidentally rolling when the vehicle is stationary and the engine is shut off.
(2) Description of Related Art
To this end, the parking lock blocks—for example, following an operation initiated by the driver—the driven transmission shaft which is non-rotatably connected to the drive wheels, typically through engagement of a locking pawl arranged in the automatic transmission with teeth of a parking lock wheel arranged on the driven transmission shaft.
Various mechanical, electro-hydraulic as well as electromechanical systems are largely known in the art as a transmission device between such parking lock implemented, for example, as a locking pawl and the operating device for the vehicle transmission arranged in the passenger compartment of the automobile. Mechanical transmission devices for operating the parking lock include, for example, a Bowden cable disposed between the selection lever arranged in the passenger compartment and the transmission control arranged on the automatic transmission.
To improve the structural design with respect to the unrestricted arrangement of the actuator in the passenger compartment and to ensure acoustic decoupling between the actuator and the drive train of the automobile, modern automobiles or automatic transmissions have increasingly transitioned to the shift-by-wire principle, since modern automatic transmissions are more and more fully electronically controlled.
The shift commands in these “shift-by-wire” transmissions are typically transmitted from the operating device and/or from the selection lever of the automatic transmission exclusively by way of electrical or electronic signals. In other words, with respect to the parking lock, the parking lock is typically also operated electrically or electro-hydraulically. However, in certain situations, the parking lock can also be operated automatically, for example when Auto-P is engaged, i.e., when the parking lock engages automatically after the ignition key is pulled out or when exiting the automobile.
The parking lock of shift-by-wire-operated transmissions is frequently engaged mechanically in by way of a spring energy store, whereas the parking lock is typically disengaged hydraulically by way of the oil pressure circulation of the automatic transmission. To prevent the parking lock from being unintentionally engaged, for example in the event of a faulty transmission oil supply, as long as the operating stage “P” is not being engaged on the selection lever, an additional locking device must be provided for the parking lock, which prevents engagement of the parking lock by using the force from the spring energy store in the transmission at least until the selection lever has been brought into the operating stage P or Auto-P.
More particularly, these locking devices for parking locks demand the smallest possible actuating force or actuating energy accompanied by high locking forces, as well as additionally a high degree of safety against faulty actuation, for example caused by vibrations, dirt or temperature changes.
Several control elements of the generic type for parking locks with locking devices are known in the art. Reference is made particularly to the documents DE 10 2008 000 857, DE 10 2005 002 448 A1 and DE 10 2006 039 862, each of which discloses control elements for parking locks with locking devices. The operating devices and locking devices disclosed therein each have a toggle lever, which is brought into an almost outstretched position for locking the parking lock in the disengaged position. Due to the kinematics of the toggle lever, relatively high locking forces can be combined with comparatively small release forces.
One characteristic property of these conventional locking devices is that particularly the toggle lever devices must be manufactured with precise tight tolerances, in order to safely implement the desired large quotient between locking force and release force. The employed toggle lever locks may also respond to different ambient conditions and must thus be protected, in particular, from contamination and strong vibrations.